Electrophotographic imaaging processes and techniques have been extensively described in both the patent and other literature. Generally, these processes have in common the steps of employing a photoconductive insulating element which is prepared to respond to imagewise exxposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well-known in the art, can then be employed to produce a permanent record of the image.
Various types of photoconductive insulating elements are known for use in electrophotographic imaging processes. The use of two or more active layers in a photo-conductive element has been discussed in the patent literature. Such multi-layer photoconductive elements are sometimes referred to hereinafter simply as "multi-active" photoconductive elements.
Co-pending Mey, U.S. Ser. No. 641,058 filed Dec. 15, 1975, discloses a multi-active photoconductive insulating element having at least two layers comprising an inorganic photoconductor-containing layer in electrical contact with an aggregate photoconductive layer. Copending Berwick et al., U.S. Ser. No. 639,039 filed Dec. 9, 1975, discloses a multi-active photoconductive insulating element having at least two layers comprising an aggregate or charge generation layer in electrical contact with an organic photoconductor-containing or charge-transport layer. The aggregate photoconductive layer of both Mey and Berwick et al., include a continuous electrically insulated polymer phase having dispersed therein a finely divided, particulate co-crystalline complex containing at least one pyrylium-type dye salt and at least one polymer having an alkylidene diarylene group in a recurring unit.
The aggregate layer used in both Mey and Berwick et al. are of the type described in Light, U.S. Pat. No. 3,615,414. Typically, it has its principle absorption band for radiation in the visible region of the spectrum within the range of from about 520 nm to about 700 nm. Within this range the aggregate layer provides an exceptional level of sensitivity. However, below 520 nm, especally in the region of 460 nm, the aggregate layer exhibits low absorption thereby lowering the overall efficiency of such multi-active elements for white light exposure as well as decreasing the ability of such elements to discriminate red copy from a white background. Clearly, there exists need in the art for multi-active photoconductive elements comprising an aggregate photoconductive layer which has greater sensitivity in the region of the visible spectrum below about 520 nm especially in the blue region of the spectrum around 460 nm.